1. Field of the Invention
The present invention relates to a center mechanism of a tire curing press which holds and lifts a bladder assembly and, more particularly, to a center mechanism which is able to easily mount and remove the bladder assembly.
2. Description of the Related Art
As this type of center mechanism of a tire curing press, a center mechanism shown in FIG. 5 has been known.
FIG. 5 shows a green tire 36 under forming by curing with the green tire 36 placed in between a lower mold 33 fixedly installed on a base frame 31 through a lower mold mounting member 32 and an upper mold 35 which can be closed and opened in relation to the lower mold 33 and with both the molds 33 and 35 closed. A center mechanism 37 is mounted through a guide sleeve 38 at the central section of the lower mold mounting member 32. This center mechanism 37 is composed of a lift cylinder 39 vertically movably inserted in the guide sleeve 38, a piston rod 40 vertically movably inserted the lift cylinder 39, and a bladder assembly 50 with the upper end of a bladder 45 held between an upper clamp ring 46 and an upper bead ring 47 and with the lower end held between the lower clamp ring 48 and the lower bead ring 49. At the central section of the upper clamp ring 46 is formed a stepped projecting section 46a; and split-type rod clamp 55 having a stepped projecting section 55a which engages with the above-mentioned stepped projecting section 46a is connected by a bolt 56, and is fastened by a bolt 57 to the upper end of the piston rod 40, thereby removably mounting the upper clamp ring 46 on the upper end of the piston rod 40. On the inner periphery of the lower clamp ring 48 is formed an internal thread section 48a. This internal thread section 48a, engages with an external thread section 60a formed on the outer periphery of the clamp ring hub 60 which is fixedly installed on the upper end of the lift cylinder 39, thus removably mounting the lower clamp ring 48 to the lift cylinder 39. The clamp ring hub 60 is provided with a supply-discharge hole 60b for leading a thermal pressure medium, such as steam, hot gas, etc., into the bladder 45 from a thermal pressure medium supply-discharge pipe 61.
Next, the mode of operation of the tire curing press and its center mechanism described above will be explained. The bladder 45 is tensioned in an extended state with the lift cylinder 39 placed in the bottom position and with the piston rod 40 placed in the top position, then the green tire 36 is inserted into the lower mold 33. After the insertion of the tire 36, the piston rod 40 is lowered to move the upper clamp ring 46 downward until the bladder 45 conforms to the inner surface of the tire 36 while being curved and deformed. Then, a thermal pressure medium is injected into the bladder 45 to fully expand, for shaping, the bladder into close contact with the inner surface of the tire 36. Subsequently, the upper mold 35 is closed to the lower mold 33 and applied, for forming by curing with the pressure of the pressure cylinder which is not illustrated. After the cure, the upper mold 35 is opened and retreated to allow the lift cylinder 39 to move upward together with the piston rod 40, and then the tire 36 is separated and raised off the lower mold 33. Subsequently the piston rod 40 is moved upward, while the lift cylinder 39 is moved downward, thus pulling out the bladder 45 from the inner surface of the tire 36 with which the bladder 45 is in close contact. Next, this post-cure tire 36 is taken out upward by means of a tire unloader or other means not illustrated, being discharged out of the curing press.
The center mechanism of the tire curing press described in the related art, however, has the following disadvantage that when mounting the bladder assembly 50 to, and removing it from, the center mechanism, the upper clamp ring 46 is bolted to the upper bead ring 47, and the lower clamp ring 48 turned to engage the thread section 48a with the thread section 60a, attaching or detaching the lower clamp ring 48 on the lift cylinder 39. This operation, carried out in a limited space, however, requires much time and labor. This bladder 45, undergoing repeated expansion and deformation at every curing cycle under a high-temperature and high-pressure environment, requires replacement with a new part every 5 to 8 days.